Generally, when an electronic device downloads content, a server providing the content may encrypt it using a specific encryption key. Once the server transmits the encrypted content and the encryption key to the electronic device, the electronic device may decrypt the encrypted content using the encryption key and then output the decrypted content on a display. In some cases, the content is transmitted from the server to the electronic device unencrypted, and the electronic device is configured to automatically encrypt the content prior to storage thereof in memory, so as to prevent the end user from making unauthorized copies. (Herein, the electronic device receiving the content may also be referred to as an end user device.)
Various encryption methods may be used by the server or electronic device to encrypt a content file. The electronic device may encrypt the content file using an encryption key and an encryption form which are defined in a Digital Rights Management (DRM) protocol, or encrypt the content file using an encryption algorithm such as an Advanced Encryption Standard (AES) or Data Encryption Standard (DES).
When an encryption key table managed by the server or electronic device is transferred to an unauthorized electronic device together with the encrypted content file, the unauthorized electronic device may decode and use the encrypted content file using the encryption key table.